The mirrorback spider is a spider that spawns in the second phase while fighting Araxxor on the top path. They may also spawn on the third phase if the player took the middle/bottom path while the top path was available or on phase four if players used the top path and skipped it. A mirrorback spider will also spawn for 10 seconds when a player with any Noxious weapon uses its special attack.

For the mirrorback spiders that Araxxor summons, any damage Araxxor would take (including AoE attacks) will be fully reflected back onto the player. Damage inflicted on the spider will also hurt Araxxor for half the damage that the mirrorback spider took. Should the hit deal more than the health the spider has, damage reflected on Araxxor will be how much the hit would have done. If a player hits 12,000 on the spider (it would deal 3,000 to the spider), Araxxor will take 6,000 damage rather than 1,500.

For the mirrorback spider players summon, successful attacks against the user will reflect half of that damage back onto the attacker, and half onto the spider. The player summoned mirrorback spider cannot be attacked directly by other players.

Killing Araxxor with reflected damage from a mirrorback spider he summons is a requirement to unlock Gavin.

Once an araxyte pet has been obtained, a mirrorback spider will spawn from an egg at the end of the top path. This spider does not count towards the 20 spiders Araxxor summons and will continually appear until Araxxor is "killed" from the reflected damage by the spider.